Re: revivesa status 2008/07/09

[Andrew Doran <andrew%hairylemon.org@localhost>]

On Thu, Jul 10, 2008 at 11:39:12AM -0700, Bill Stouder-Studenmund wrote:
> On Thu, Jul 10, 2008 at 10:28:44AM +0300, Andy Shevchenko wrote:
> > On Thu, Jul 10, 2008 at 9:31 AM, Bill Stouder-Studenmund
> > <wrstuden%netbsd.org@localhost> wrote:
> > > Today's code (actually last weekend's; I've been AFK for a bit) now passes
> > > all of the NetBSD 4.0 libpthread regression tests! As such, I think the
> > > branch is an overall success.
> > What about VSTHlite to be included to the bunch of regression tests?
> > Some discussion about it here:
> > http://mail-index.netbsd.org/tech-misc/2008/06/24/msg000046.html
> 
> That's a separate discussion. The goal of the revivesa branch is to 
> implement support for the Scheduler Activations system calls used by the 
> SA libpthread in NetBSD 4.x.

It has to be said, I have not seen a convincing explanation as to why this
is desirable or in the best interests of NetBSD as a product.

SA threading in NetBSD has serious problems and drawbacks. For example:

- it works only on a handful of architectures, eg x86.
- in most tests its performance is demonstrably inferior to 1:1.
- it's completely unreliable, even opening the machine to DOS attacks.
- it has architectural, code quality and code maintenance issues.
- it completely lacks any kind of real-time support.

In its current form SA threading is a regressive proposition. Even if all
the remaining issues are addressed, what benefits would it bring over and
above 1:1 threading?

Andrew